The invention relates to an evaporator for a motor vehicle air conditioning device.
The evaporator, connected to the rest of the air-conditioning circuit of a motor vehicle, has the function of cooling a ventilation fluid intended to be blown into the vehicle interior. In general, the ventilation fluid is air from outside the vehicle.
The evaporator thus comprises a plurality of refrigerant tubes inside which a refrigerant fluid circulates. On contact with these refrigerant tubes, the ventilation fluid gives up some of its calories to the refrigerant tubes and is therefore cooled. The fluid is made to circulate inside the air-conditioning circuit by a compressor usually driven by an engine of the motor vehicle.
Therefore, when the vehicle engine is switched off, the circulation of the refrigerant fluid in the device no longer takes place and the exchange of heat between the air and the refrigerant fluid can no longer take place. The air blown into the vehicle interior is then no longer cooled. This situation is all the more problematical when fuel economy systems plan for the engine to be switched off automatically when the car is stationary, thus preventing the air-conditioning device from operating.
It is known practice to provide the evaporator with a reservoir of thermal storage material. During engine operation, the refrigerant fluid circulating in the evaporator simultaneously cools the air passing through the evaporator and the reservoir of thermal storage material. When the engine is switched off, the thermal storage material releases the frigories previously accumulated in order to cool the air passing through the evaporator. It will be recalled that, by analogy with a calorie, a frigory corresponds to the amount of heat needed to reduce the temperature of one gram of water by 1° C. from 14.5 to 15.5° C. under standard atmospheric pressure.
It is also known practice to use, by way of thermal storage material, a phase change material referred to by the abbreviation PCM. When the PCM is in contact with the refrigerant fluid, it solidifies. When the engine is switched off, the PCM liquefies and therefore releases frigories to the air passing through the evaporator.
It is known practice to arrange the PCM in tubes with a checkerboard geometry associated with refrigerant tubes likewise arranged in a checkerboard configuration.
However, with this arrangement, the distribution of the pressures within the tubes is heterogeneous. It is therefore necessary to manufacture tubes which are thicker in order to withstand this difference in pressure, and this makes the evaporator heavier.
Examples of evaporators equipped with storage members comprising pluralities of housings forming reservoirs of phase change material are also known from applications US-2010 307 180, JP-2011 201 328 and JP-2012 037 900.
The evaporators divulged have the disadvantage of not solidifying the PCMs homogeneously and completely in a sufficiently short space of time when the engine of the vehicle is in operation. Thus, it is possible that the PCMs might not be completely solidified when the vehicle stops, for example at a red light, and that they might not be able to cool the air blown into the interior for a sufficiently long length of time. In addition, the heat exchangers between the refrigerant fluid and the housings forming reservoirs of PCM are somewhat inefficient because the PCM reservoirs need to be provided with fins the task of which is to improve the efficiency of the heat transfer. These fins make the evaporator heavier. Furthermore, because of the arrangement of the PCM reservoirs in the evaporator, the ventilation fluid experiences mechanical friction as it passes through the evaporator. This mechanical friction results in pressure drops.
It is therefore an object of the invention to overcome these disadvantages.